Leaf stains

>Plant-edders,
> Walking across campus I notice the familair leaf stains on concrete
>sidewalks. Some are very good images and show perfect leaf outline and
>even major venation. I asked my Plant Phys class how they occur.
> Now, I need to make sure I have an answer. This doesn't occur with green
>leaves. I am assuming that water is leaching some pigments, tannins, etc
>out of the leaf. Either chlorophyll isn't soluble, doen't stain, or
>remains within a living leaf. What is it that is staining the concrete?
>It is apparently water-soluble.
Obviously, Jack Frost has had to comply with some pretty strict new EPA
guidelines relating to the formulation of his paints. Sounds like what he's
using this season isn't quite as waterproof as the "old stuff."
Seriously, I have never seen anything like this! Is it all the colored
leaves, or just a few species?
Monique in fall-color-deprived Texas